Rolls used to convert, and particularly to emboss, cellulosic fibrous structures are well known in the papermaking art. Converting refers to any post drying operation which permanently affects any property of a cellulosic fibrous structure. Converting rolls typically have a pattern of radially extending protuberances which imparts the emboss pattern to the cellulosic fibrous structure. Each roll may be integral, or may be constructed from a plurality of components assembled in a particular configuration.
A roll made from an integral assembly typically has the periphery of the roll, between the protuberances, chemically etched away, to leave only the radially extending protuberances unaffected by the etching process. The protuberances may then be machined to the final dimensions with a great deal of accuracy.
However, such an etching process leaves the periphery of the roll between the proximal ends of the protuberances: out of tolerance with respect to straightness, concentricity, and diameter. Because this periphery of the roll is not a close tolerance surface and may be out of tolerance with respect to the foregoing parameters, the roll may be unsuitable for use in manufacturing which requires a great deal of accuracy at the roll periphery.
Because the periphery of the roll is not a close tolerance surface, the periphery of the roll may be unsuitable for and hence is not used in the manufacturing process. This unsuitability represents a great waste, because, frequently, the periphery of the roll between the protuberances represents the majority of the surface area of the roll and the protuberances represent only a small percentage of the total surface area of the roll.
Various attempts in the art to provide rolls constructed as an assembly have not been successful in overcoming this waste. For example, certain attempts in the art disclose magnetically attached flexible plates to the surface of an embossing roll. The plates may be removed and replaced as desired. Other attempts have utilized interference fits to assemble the components of the roll. Examples of such attempts in the art include U.S. Pat. Nos. 4,116,594 issued Sept. 26, 1978 to Leanna et al. and 4,705,711 issued Nov. 10, 1987 to Perna.
Also attempts have been made in the art to widen the compressive zone of the nip between rolls, or to permit deflection of rolls when a fabric passes between the rolls. The art further teaches coating the roll to achieve proper compliance and hardness. Yet other attempts in the art include a roll having a telescoping assembly which permits water to drain through. Examples of such attempts in the art include U.S. Pat. No. 4,559,106 issued Dec. 17, 1985 to Skytta et al.; U.S. Pat. No. 4,856,159 issued Aug. 15, 1989 to Skytta; U.S. Pat. No. 4,868,958 issued Sept. 26, 1989 to Suzuki et al.; and the aforementioned U.S. Pat. No. 4,705,711 issued Nov. 10, 1987 to Perna.
However, none of these teachings overcome the problems of obtaining highly accurate protuberances in a roll with a close tolerance periphery between the protuberances. To achieve two close tolerance surfaces, the roll may be assembled from separate components. Each of the separate components may be machined to the desired tolerance prior to assembly. The prior art does not even teach how to assemble such a roll, even if close tolerance components were available. Furthermore, because the prior art has not utilized such a roll, the prior art does not teach the use of such roll to eliminate the waste which has heretofore been present without such close tolerance rolls being available.